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IB ESS HL 2.1.23 Keystone Species Questions

Prepare for IB ESS HL 2.1.23 by analysing how keystone predators and herbivores shape community structure, biodiversity and resilience through trophic cascades.

Syllabus
First assessment 2026
Course
ESS HL
Level
HL

Exam points

  • analyse how keystone species control populations and community structure using an elephant, otter or wolf example
  • predict vegetation, habitat and biodiversity changes after removing a keystone predator or herbivore
  • explain how predator regulation supports resilience through productivity, biodiversity and food-web complexity
  • evaluate whether losing a large species threatens stability and biodiversity using a keystone-species judgement

Learn this topic

Study 2.1.23—Keystone species conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

IB ESS HL 2.1.23 Keystone Species Questions question 1

[Maximum number: 4]
Figure A simplified food web in a kelp forest ecosystem

Figure A simplified food web in a kelp forest ecosystem

Figure Kelp forest ecosystems with and without the presence of sea otters

Figure Kelp forest ecosystems with and without the presence of sea otters

The arrows indicate the flow of carbon between the atmosphere and the carbon stored in kelp.

Question (a)

(a)

Outline why sea otters are considered a keystone species.

[ 1 ]

Question (b)

(b)

Explain how sea otters contribute to the resilience of the kelp forest ecosystem.

[ 3 ]
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